How does SQL Server compress NULL bit data types?

Question

Possible duplicate:
Can Microsoft store three-digit fields in one bit?

According to the documentation for bits , the data type of a bit can have three values: 0, 1, and NULL, and if there are 8 or fewer bits in the table, these columns will be compressed into one byte.

These two behaviors seem contradictory. If so, which part is correct, the ability of bits to be NULL, or compression of 8 bits per byte?

Answer 1

NULL values ​​are processed by a separate bit for each column (for example, see here ).